2 comments to Super-Sized Moons Common?

The Roche limit has to do with whether matter is far enough away to coalesce into a moon in the first place. At or below the Roche limit it will fail to coalesce and form rings.

I think the standard model of planetary formation predicts that all rings should eventually fall out of orbit. The reason Saturn and Jupiter still have rings after all this time seems to be because of the shepherd moons, or because they keep being fed by something. Saturn and Jupiter also have moons within the Roche limit, however, which is a bit of a mystery. As does Mars, though Phobos is probably a captured asteroid that’s expected to become ringified eventually.

I do wonder about the accuracy of our planet-formation models sometimes, given that we only have eight concrete data points to base them on, and that our real planets all seem to violate the very rules we make to explain how they should have formed.